What Is a Nuclear Core Meltdown?

Nuclear reactors provide about 15 percent of electricity generation worldwide, including 20 percent in the United States. Concerns about the safety of reactors, especially fears about a nuclear core meltdown, have stopped construction of new reactors.

Nuclear Reactors

• Nuclear reactors use radioactive fuel, such as uranium oxide pellets, which break down in a process known as nuclear fission. In turn, this energy produces heat, which is used to power steam-driven generators to create electricity. The parts of a nuclear reactor include its fuel, moderator and control rods to regulate the amount of energy released, a coolant to keep the core from overheating, a containment structure and the steam generator.

Core Meltdown

• The reactor core is where the uranium fuel undergoes fission. The energy released produces large amounts of heat. Keeping the reactor core cooled it vital, because heat can build to dangerous levels and melt the fuel. This melting can cause the containment structure to fail and release radioactive elements into the environment.

Dealing With an Emergency

• Local and state governments and federal agencies have procedures in place to deal with nuclear emergencies. FEMA defines two emergency planning zones; the first is within 10 miles of a nuclear power plant and the second is within 50 miles of the plant. People within 10 miles of a nuclear power plant are most likely to be directly affected by radiation, while farther out contamination is most likely.